1. Field
One embodiment of the present invention relates to a disk drive, and more particularly to a technique for measuring an offset between a read head and a write head using a disk as a discrete track medium.
2. Description of the Related Art
Recently, in a disk drive typically represented by a hard disk drive, attention is paid to a discrete track medium (DTM) type disk as a disk which is a magnetic recording medium. In the DTM type disk, a pattern is formed on a substrate, and the pattern has a magnetic region, which is a magnetic recording region of data, and a non-magnetic region (nonmagnetic guard band) which are separated from each other. The disk drive positions a magnetic head on a designated magnetic region and records data or reproduces recorded data. The magnetic region in which data is recorded may be called a data track.
The magnetic head has a structure in which a read head and a write head are separately mounted on one slider (head body). The read head is a head for reading out data from on a disk. The write head is a head for writing data onto the disk. In the magnetic head having the structure described above, an offset exists between the read head and the write head. Accordingly, a certain amount of offset (positional dislocation) occurs in a track locus of each of the read head and the write head depending on a radial position on a disk medium.
In a disk drive, when a magnetic head is positioned to a position designated on a disk, an offset control is executed to each of a read head and a write head to perform a positional adjustment based on a measured offset value. In the offset control, a dynamic offset control (DOC) is effective which executes a control using an offset value which changes when a disk rotates once in consideration of a disk runout and the like (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-216378).
To measure an offset value necessary to an offset control, there is conventionally proposed a method of calculating an offset value by recording data for measurement on a DTM type disk and reading out the data for measurement by a magnetic head (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2007-265546).
As described above, as a method of measuring the offset value with respect to the DTM type disk, there is a method of calculating the offset value by recording data for measurement on a disk and reading out the data for measurement by a magnetic head. In the DTM type disk, the data for measurement is written on a magnetic region formed in a pattern by a write head of the magnetic head.
However, when an offset is greatly varied when a disk rotates once due to a factor such as a disk runout and the like, there is a possibility that the data for measurement cannot be securely written on a magnetic region. In this case, a measurement accuracy of the offset value is lowered because the data for measurement cannot be read out with a pinpoint accuracy.